1. Field of the Invention
The present invention relates to a control device, a control method, a control device of a vehicle, and a control system of a vehicle that compresses binary data expressing an external varying event and records the compressed binary data.
2. Description of the Related Art
As a control device that manages binary data received successively from a plurality of electronic control units through a network, for example, a diagnostic recorder is mounted in a vehicle.
In the diagnostic recorder, of various kinds of control data transmitted at any time from respective electronic control units through a CAN bus and used for a failure diagnosis and analysis, at least the newest control data is compiled as frame data at predetermined intervals and is stored in a storage device.
The control data like this is very large in amount, so that the diagnostic recorder is usually configured to be built in a navigation system provided with a large capacity storage device such as a hard disk device and to store the control data in the hard disc.
In the diagnostic recorder, the control data of an amount of about 200 bytes is stored at one time at intervals of 500 msec and control data equivalent to at least 120 hours is required to be held.
However, the navigation system is not always provided with a hard disc device having a large capacity, and a vehicle not provided with such a large capacity storage device has the problem of difficulty in accumulating the control data.
Further, even in the case where the vehicle is provided with a storage device having a large capacity, to realize the functions of a navigation system such as the guiding of the vehicle to a destination and the outputting of images and voices to an audio-visual device, the hard disc device is required to have a storage region large enough to store a large amount of music data, image data, moving picture data, map data, and the like, which presents also such a problem that to secure a large storage region for this purposes is not desirable.
In view of these circumstances, it can be thought that the diagnostic recorder is provided with a storage device made of a semiconductor memory such as an EEPROM and that control data is subjected to a compression processing, thereby being reduced in amount and then stored.
However, a general-purpose compression processing algorithm capable of efficiently compressing a large amount of image data is an irreversible compression method and hence cannot decode the image data correctly. Thus, the general-purpose compression processing algorithm cannot be used for the compression processing of the control data.
As a reversible compression algorithm generally having a large compressing ratio, there have been proposed algorithms such as SLC (Super Lossless data Compression) employing statistical modeling and ELC (Embedded Lossless data Compression) employing dictionary-type modeling.
The statistical modeling is a method that computes the probability of a character (usually, one byte) appearing in a predetermined run of characters (context) and that assigns a symbol to the probability to thereby reduce the amount of data.
The dictionary-type modeling is a method that stores a sentence appearing in the past as it is in a RAM as a dictionary, compares a newly read sentence with the dictionary to search repetitions of characters, and assigns a symbol to a run of repeated characters assuming that the run of repeated characters is a copy of the sentence appearing in the past, thereby reducing the amount of data.
However, these compression algorithms need a working area from several tens of kbytes to several hundreds of kbytes and hence the diagnostic recorder provided with a RAM having a capacity from several kbytes to several tens of kbytes cannot employ these compression algorithms.
On the other hand, the Japanese Unexamined Patent Publication No. 6-217110 discloses the following image conversion method: that is, when an image conversion such as enlarging, contracting, or processing an image is carried out, the binary data of an input image is encoded by a byte unit of run length and the image conversion is carried out on the basis of the encoded data of the byte unit of run length.
However, the above-mentioned control data varies largely depending on the state of the vehicle such as states where the vehicle is running, idling, or has its engine stopped, so that there is presented such a problem that even if the control data is subjected to the compression processing by the use of the run length method described in the above-mentioned patent publication, a compression effect cannot be produced as much as desired.
This problem is not limited to the control device such as the diagnostic recorder mounted in the vehicle but is a problem that holds true for all the control devices for storing a plurality of pieces of binary data each having a large degree of variation in a storage portion by the unit of a frame at predetermined time intervals.